Login a gg account in microG adds gg’s account to the phone (test with SNCF, in french). So, the ‘best’ solution is to install /e/ without SIM card, add a gg account, install apps wich need it, remove the gg account, insert SIM.
But I think gg has already IMEI and device serial n° and so on…
With Shelter, install WhatsApp doesn’t create a WA account on pĥone, but I couldn’t restore local backup (toast notif. ‘W.A. needs goolag services, witch are updating’). I think (will test, later) gg-dependents apps won’t work sandboxed because gg account seems to link a number of system apps (with ./folders I don’t know how to find/remove).
Édith says ‘Youtube-dl’ (I use for private copy) has its own repo for quick-update mode (as #root), because youtube’s rules move permanently. Perhaps a way to the microg project, its own repo and simple update-upgrade mode to allow upgrade without re-compile each ROM ?..